Add an OCE_SKIP_TESTS_DATA environment variable when running OCCT tests

This variable let locate_data_file exits quickly, as we know we
do not have data files.  This speeds up processing SKIPPED tests.
Do not set CSF_TestScriptsPath environment variable

Tests are already searched in the $CASROOT/tests directory; by setting
CSF_TestScriptsPath, tests are run twice.